1. Field of the Invention
The present invention relates to a microchip, and specifically relates to a microchip for detecting a reaction of a specimen and a reagent, e.g., a microchip suitable for use in blood clotting examination, immunological examination, biochemical examination, genetic examination and the like.
2. Description of the Related Art
Conventionally, devices using a light scattering detection method and devices using a magnetic sensor detection method are known as devices which, for example, measure clotting reaction in blood.
In a device using the light scattering detection method, as shown in FIG. 11 for example, light 5a from a light source 5 irradiates a cuvette 7 containing a liquid mixture of specimen and reagent, and the scattered light 5b from the specimen and reagent liquid mixture is detected by a sensor 6. The specimen can be examined because the reaction of the specimen and reagent and the intensity of the detected scattered light 5b have a constant correlation. This device detects a change in the static liquid mixture, and its efficacy is reduced by blood turbidity and noise induced by bubbles generated when the specimen and reagent is mixed.
In a device using the magnetic sensor detection method, as shown in FIG. 12 for example, a cuvette 7′ containing a mixture of specimen and reagent and a steel ball 8 is rotated about an axis slightly inclined from the vertical, and the movement of the steel ball 8 is detected by magnetic sensor 9. For example, when the viscosity of a mixture is changed by the clotting of blood, the change in viscosity of the mixture is detected using the movement of the steel ball 8 settling to the bottom. In this device, the cuvette 7′ must be rotated, and minute changes in viscosity cannot be detected.
Such conventional devices (large devices) require the collection of a certain amount of blood. Since these are immobile devices that cannot be carried, they do not correspond to point of POC (point of care, i.e., place of treatment). Furthermore, there are limits to reducing examination time and improving accuracy. They also produce large amounts of waste.
Recently, attention has focused on μ-TAS (μ-total analysis system) for miniaturizing devices and methods such as chemical analysis and synthesis and the like. This system is realized by an applicative of micro-machine technology. Advantages of miniaturized μ-TAS include the use of small amounts of sample, reduced reaction time, and less waste product compared to conventional devices. Furthermore, when applied to the field of health care, it is expected to reduce the burden on patients by using a small amount of specimen, and lower the cost of examination by reducing the amount of reagent.
For example, Roche Diagnostics K.K. (Tokyo, Japan) has sold CoaguCheck Plus, a device which uses a microchip for mixing blood and reagent as the blood flows within a reagent chamber by capillary action, and capture the stoppage of flow of blood as a change in scattered light, and measure the time until the flow stops.
This device, however, requires an expensive microchip because a dry reagent (a regent solidified to the microchip) is used although the specimen amount is rather small at only several tens of micro liters. Furthermore, measurement accuracy of the device cannot be said so good as those of the conventional large-scale devices.